LESSONS IN CHEMISTRY. 



101 



generally those (1) On a piece of charcoal, in which a little cap 

 has been hollowed in order that the oxide may not bo blown 

 away ; ('2) in a small clay or platinum cup ; (3) when the 

 action with borax or microcosmio salt is required, a piece 

 of platinum wire is thrust into a rod of glass, when its end 

 is fused, the other end of the wire being booked, as in Fig. 

 53. Platinum and glass have almost the same coefficient 

 of expansion, so that the glass does not crack when it 

 cools. The wire is heated, then placed in the borax, etc., 



n which adheres to the hot wire ; this is now introduced 

 into the flame, and immediately swells up, but soon be- 

 comes a clear bead surrounding the hook of the wire. 

 When in this state it is touched with the body which 

 is to be tested, and again introduced into the flame. 

 The following table, which is condensed from Conington's 

 "Handbook of Chemical Analysis," gives concisely blow- 

 pipe teats, h signifies hot ; c, cold ; supers., that the 

 bead ia supersaturated with oxide; not sat., that it is 

 not completely saturated with oxide. 



WITH MICEOCOSMIC SALT (Na,NH 4 ,H,P0 4 ). 



WITH BORAX (Na,H,BO s ). 



COLOUE OF 

 BEAD. 



IN OXIDISING FLAME. 



Silica, Alumina. Supers, 

 opaque : alkaline earths 

 Colourless. \ and earths. Silter oxide. 

 Not sat. : Zn, Cd, Pb, Bi, 

 and Sb oxides. 



Yellow or 

 Brownish. 



Bed. 



h. not sat., Ferric and 

 Uranic oxides, h. supers., 

 Pb, Bi, and Sb oxides. 



h. Ferric oxides. 



c. Nickel oxide (red-brown). 



h. supers., Chromic oxide. 



Violet or .Manganic oxides. 

 Amethyst. Nickel, containing Cobalt. 



Blue. 



! Cobalt oxide, 

 c. Cupric oxide. 



Green. 



Grey and 

 Opaque. 



c. Chromic oxide, h. Cupric 

 oxide, Ferric oxide, con- 

 taining Cobalt or Copper. 



IN REDUCING FLAME. 



Silica, Alumina, Stannic 

 oxide. Supers., opaque : 

 Alkaline earths and earths, 

 .Manganic oxides, h. Cupric 

 oxide. 



c. Cupric oxide. 



Ctbalt oxide. 



Ferric and Chromic oxides. 



As with Microcosmic Salt, 

 and with Nickel oxide. 



tf the analysis of a compound substance be required, the 

 works of Fresenius or Conington must be consulted ; but if it bo 

 required to determine the quality of a single substance, such as 

 the salt or oxide of a metal, the following tables will serve to 

 direct tuo inquiry. In all cases, it must be remembered, the 



substance matt be in a solution. All metallic bodies will be 

 dissolved by concentrated or dilute hydrochloric or nitric Mid, 

 or aqua-regia. In most cases, water ia a solvent of salts reduced 

 to powder; some of the chief bodies which are insoluble are 

 thus rendered soluble. 



Silicates fuse with four parts of alkaline carbonate ; the sub- 

 stance is now capable of solution in hydrochloric acid. 



The sulphates of barium and strontium are similarly fused with 

 alkaline carbonate. The result when digested in water gives 

 its acid to the water with the alkali, and leaves the base, 

 which is soluble in hydrochloric acid. 



When sulphate of lead is thus treated, a metallic globule is 

 found, thna indicating the nature of the body without further 

 search. 



Fluorides, when treated with concentrated sulphuric acid, 

 evolve hydrofluoric acid gas, which etches glass. They are 

 rendered soluble as silicates, and when digested with hot water, 

 the water takes up the acids, leaving behind the bases, which 

 are now soluble in hydrochloric acid. 



Aluminates are rendered fusible by the same treatment. 



THE ALKALIES. 



THE ALKALINE EARTHS. 



The preceding oxides give no precipitates with ammonia or 

 ammonium sulphide, like the following group : 



